Chlorinated oxetane polymer coating composition



problem of long standing United States Patent cc 3,409,623 CHLORINATEDOXETANE POLYMER COATING COMPOSITION Lester W. Smith, Berwick, Pa.,assignor to ACF Industries, Incorporated, New York, N.Y., a corporationof New Jersey No Drawing. Continuation-impart of application Ser. No.366,614, May 11, 1964. This application Mar. 5, 1965, Ser. No. 437,558

7 Claims. (Cl. 26029.2)

ABSTRACT OF THE DISCLOSURE A coating composition adapted for applicationto the interior of large vessels and railway tank cars comprises adispersion of a finely divided chlorinated polyether polymer in anaqueous medium including water, a assurfactant, and an ester of apolyhydric alcohol such as ethylene glycol diacetate; the compositionmay also include a lower aliphatic alcohol and a water softener. Asimilarly suited primer coating composition comprises a dispersion of afinely divided chlorinated polyether polyrner in a non-aqueous organicdiluent, such as methylene chloride, a chlorinated aliphatichydrocarbon, and an ester of a polyhydric alcohol. The composition isapplied by maintaining the surface of the material to be coated aboveabout 50 F., spraying the composition onto the surface and then dryingand curing at a temperature between about 380 and 450 F., followed bycooling the coating.

This application is a continuation-in-part of copending application Ser.No. 366,614, filed May 11, 1964.

This invention relates to a novel system for the protective coating ofmetal surfaces with chlorinated polymers. More particularly, theinvention concerns novel chlorinated polyether dispersions, and themethods of preparing and applying them to metals.

The protection of metal surfaces against corrosion and abrasion bymaterials and against mechanical injury by tools and other articles bywhich they are contacted is a in the process industries and in thetransportation field. In industrial plants it is necessary to protectthe surfaces, and particularly the interior surfaces, of storage andprocessing tanks, piping, ducts, pumps, meters, and other equipment,against these influences. A similar need for protection is found inmanufacture and utilization of containers and tank cars for thetransportation of solid and liquid commodities, such as chemicals, fats,oils, powders, food products, and the like. In both industry andtransportation, the aim has been to provide a protective coating whichwould be resistant to a broad spectrum of materials, and which would atthe same time withstand elevated temperatures, and present a smooth anddependably adherent film on the metal. This goal is of specialimportance in the tank car field, for in the mass transportation ofmaterials, considerations of economy demand the use of large vessels,whether of tank car size or of less-than-carload dimensions. Since abroad range coating material has not heretofore been available in a formwhich would fully meet the requirements of corrosion and abrasionresistance and also possess the necessary ease of application, adherenceto the metal substrate, resistance to shock and vibration and longservice life, it has been necessary to employ special metals or specialcoatings to meet each type of service requirement.

A class of compounds which is characterized by chemical inertness, andwhich can be applied as a thick continuous adherent film which isresistant to abrasion, thermal shock, and mechanical injury, isrepresented by Patented Nov. 5, 1968 the chlorinated polyether polymers.Typical of this class of polymers ispoly[3,3-bis(chloromethyl)-oxetane], Which is sold commercially underthe designation Penton by Hercules Powder Company, Wilmington, Delaware.These chlorinated polyether polymers are crystalline thermoplasticmaterials having a high chlorine content of about 45%, and a meltingpoint above about 350 F., depending upon the degree of polymerization.The product known as Penton has a melting point of 375 F and an averagemolecular weight between about 250,000 and 400,000.

Chlorinated polyether polymers are chemically inert and resistant tosolvents at relatively high temperatures. In view of the small number ofavailable solvents, such as, for example, cyclohexanone (all of whichare such weak solvents that the solution produced is uneconomical anddiflieult to apply), it has been proposed to apply chlorinated polyetherpolymers as coatings by forming a suspension of fine particles of thepolymer in an aqueous medium, applying the suspension to the metal,drying the suspension in place, and then fusing the resin to form acoating layer on the metal surface. In one coating system of this type,the resin is kept in suspension by means of a combination of a cationicflocculating agent, such as a long chain fatty amine and a bindingagent, such as pectin or a starch derivative. However, in the knownchlorinated polyether polymer coating systems, it has been difficult toobtain coatings of sufiicient thicknesses and imperviousness to protectmetal surfaces against corrosive agents for long periods of time.

In accordance with the invention, there are provided novel chlorinatedpolyether polymer dispersions which are characterized by ease ofpreparation and application, and a high degree of stability. Thedispersions are capable of being applied to metal surfaces byconventional techniques, but are especially adapted to application byair spraying. The improved dispersions permit relatively thick coatingsto be sprayed without running or sagging, they dry more readily in placeon the metal surface, and after fusion they form continuous, stronglyadherent, corrosion protecting films which possess long life, and whichresist vibration and shock.

These characteristics are particularly significant in regard to theinterior coating of large vessels and railway tank cars, which have notbeen coated successfully with chlorinated polyether polymers prior tothe present invention.

The dispersion of the invention includes as its film forming component achlorinated polyether polymer, which is selected so that its degree ofpolymerization and its melting point will assure the formation of aresinous film which will, upon curing, produce a hard, impervious, andadherent coating. The preferred chlorinated polyether polymer is thatwhich is sold commercially under the designation Penton, as previouslyindicated, but it is to be understood that while this polymer will beemployed herein to illustrate the practice of the invention, theinvention is not to be considered as limited thereto.

The chlorinated polyether polymer is employed in finely divided form,but the improved method of dispersion of the invention permits the useof the polymer in a less finely divided state than the minus 200 meshparticle size which has been characteristic of previously employedsuspension producing methods. In the practice of the invention, thechlorinated polyether polymer is preferably utilized as a powder, thecoarser particles of which all pass a US. Standard 60 mesh sieve, andthe preponderance of which, namely preferably 60% or more, pass througha US. Standard mesh sieve. It has been found, in accordance with theinvention, that this particle size range facilitates the formation ofstable dispersions employing the technique disclosed herein, but theparticle size range is not to be regarded as critical, since finer sizesmay be employed, if desired.

The chlorinated polyether polymer is available commercially in both thenon-pigmented and pigmented forms, but for the purposes of the inventionthe non-pigmented form is preferred.

In accordance with the invention, there is employed as a dispersionmedium, an aqueous vehicle including as its principal ingredients (a) asurfactant, (b) an alkaline water softener, (c) an ester of a polyhydricalcohol, and (d) water.

These ingredients are blended until a homogeneous solution is obtained.The amount of the alkaline water softener is selected so that the pH ofthe resulting solution is at least 7, although with some hard waters thevalue may rise somewhat above this figure.

The dry, finely divided chlorinated polyether polymer is added to theforegoing solution with thorough mixing until a homogeneous dispersionis of about to minutes is sufficient.

While the surfactant serves to deflocculate the polymer and to aid inits dispersion, it was found, in accordance with the invention, that itsaction is greatly enhanced by the inclusion of the polyhydric alcoholester. Although the action of the latter is not fully understood, itappears to exert a plasticizing action on the polymer, and, inconjunction with the surfactant, produces a smoothly flowing dispersion,which is capable of being sprayed, and which exhibits extraordinarystability on standing. Thus, less than 1% separation occurs when thedispersion is stored for extended periods and this separation is asupernatant liquid rising to the top which can be readily incorporatedin the dispersion. It is this greatly improved dispersion which enablesthe wet coated film when applied to the metal surface to maintain itsintegrity to an extent heretofore unobtainable with any knownchlorinated polyether film applied from suspension.

Another novel feature of the invention lies in the addition to thechlorinated polyether dispersion, immediately prior to spraying, of avolatile, water soluble organic diluent, whereby the drying of the wetfilm is controlled and facilitated, permitting the attainment of,a dryfilm thickness as high as 40 mils or more, in contrast with the coatingsof from 5 to 20 mils obtainable by known methods. This represents animportant technological advance in comparison with known processes, and,for the first time, it makes possible the successful application of thistype of polymer as a single coat, with its attendant advantages, in thecoating of large surfaces, such as those of storage tanks and theinterior of railway tank cars.

In the practice of the invention, the organic diluent is blended withthe aqueous dispersion prepared as previously described, and theresulting mixture is applied to the metal by spraying or other means.

The surfactant is advantageously an anionic type surfactant, of whichthere are several well known types commercially available. It is chosento leave as little residue as possible on curing. Preferably thesurfactant is an ester of sodium sulfosuccinic acid, such as, forexample, the dioctyl ester, which is sold commercially under thedesignation Aerosol OT (American Cyanamid Company, New York). Othertypes of anionic surfactants which may be employed include sodium saltsof alkyl aryl sulfonates, such as these sold under the designationNaccono (Allied Chemical Corp., New York) such as, for example C H -C H-SO Na; and sodium salts of sulfated alcohols, exemplified bysodium-lauryl sulfate sold under various names such as Gardinol,Duponol, and the like.

The amount of surfactant required is not critical, and will generallylie in the range of about 0.0007 to about 0.08 part per 100 parts ofwater employed, said parts obtained. Usually a period 4 being by weight,and the surfactant being on the 1'00% solid basis.

The ester of a polyhydric alcohol is a water-miscible ester of ethyleneglycol or of glycerol, with an organic carboxylic acid. Both diestersand triesters are contemplated. Thus, for example, there may beadvantageously employed ethylene glycol diacetate, as well as thedipropionate and the dibutyrate. The preferred ester is ethylene glycoldiacetate, a colorless liquid having approximately 10% water solubility.There may also be employed glyceryl diacetate (diacetin), and glyceryltripropionate. The amount of ester will depend upon the desired filmcharacteristics, but will generally lie between about 10 and 20 partsper 100 parts of water.

The water employed is advantageously distilled or deionized water, buteven where water of this purity is employed, the contact of the sprayeddispersion will, on the surface of mild steel, produce some oxideformation. This may be minimized, and the alkalinity of the dispersioncontrolled, in accordance with the invention, by the inclusion of awater softener having an alkaline reaction, such as, for example, analkali metal phosphate or carbonate. Suitable examples of watersofteners include sodium hexametaphosphate, sodium metaphosphate,trisodium phosphate, and sodium tetraphosphate.

The preferred water softener is sodium hexametaphosphate, soldcommercially under the designation Calgon (Calgon, Inc., Pittsburgh,Pa.). The amount employed may vary between about 0.05 and about 0.30part per 100 parts of water present.

As indicated previously, the dispersion of the polymer, prior toapplication, as by spraying, is blended with a quantity of an organicwater soluble diluent. The diluent is preferably a lower aliphaticalcohol which is more volatile than water, such as, for example,methanol, ethanol, isopropanol, and propanol. The amount of alcoholemployed will generally lie between about 10 and about 50 parts per 100parts of water present. The preferred alcohol is isopropanol.

Where the polymer dispersion is to be applied to the surface of anoxidizable metal such as steel, the surface is preconditioned andcleaned by sand or grit blasting.

The method of application of the polymer dispersion, in accordance withthe invention, includes the steps of forming the dispersion, andspraying or otherwise applying the dispersion to the metal surface,which has been preconditioned by cleaning, and, if desired, byprecoating with a primer.

The metal temperature is maintained above about 50 F. in order to assuresmooth deposition, and the temperature of the polymer dispersion ismaintained between about 65 F. and F. The dispersion is applied untilthe desired wet film thickness has been built up, measurements beingtaken with a wet film gauge, and depressions made by the gauge arefilled and smoothed.

The thus coated wet film is then dried and cured by heating the metal toa temperature between about 380 F. and about 450 F. for about 30 tominutes. At the end end of the curing period, the metal is subjected torapid cooling (quenching) to below about 200 F. within a limited periodof time. Quenching imparts a glossy surface to the coating and tends todelay or retard crystallization, thus improving adhesion. Improperquenching results in a lack of adhesion and, consequently, anunsuccessful coating.

The dispersion of the invention may be applied by means of conventionalair spraying techniques and equipment. The spray orifice size will begenerally of the order of 0.05 inch. Thus, there may be employed a BinksNo. 18 spray gun with a No. 66 PE air cap, and a Binks 63E fluid nozzle,orifice size 0.046". A fluid pressure of about 20 p.s.i.g. and anatomizing pressure of about 30 p.s.i.g. are satisfactory and serve toexemplify the practice.

In accordance with another aspect of the invention, it has been foundthat the novel chlorinated polyether polymer coating compositions of theinvention are most effectively applied to metal surfaces in conjunctionwith a novel solvent dispersed chlorinated polyether (Penton) primer.This primer, in conjunction with the coating composition, provides acoating system which exhibits greatly improved adhesion to metalsurfaces, and which may be employed, when the primer is properlyapplied, to minimize the danger of the aqueous content of the systemrusting or corroding the base metal. The primer may be applied byconventional spraying methods and fused at elevated temperatures so thatthe resin will form a total protective coating of good integrity.Subsequent application to the primer of the aqueous coating compositionyields, upon fusion, a homogeneous film with no separation ofcoatinglayers. However, the use of the primer still necessitates properpreliminary surface preparation and conditioning.

The primer composition comprises a dispersion of a chlorinated polyetherpolymer (Penton) in a non-aqueous organic diluent. The diluent includesat least one chlorinated aliphatic hydrocarbon, examples of suchdiluents being trichloroethylene and methylene chloride. The diluentalso includes an ester of a polyhydric alcohol, such as ethylene glycolor glycerol, with an aliphatic carboxylic acid. There may beadvantageously employed ethylene glycol diacetate. The primercomposition also includes a dispersing agent which is preferably of theanionic type,

the preferred agent being an ester of sodium sulfosuccinic acid, suchas, for example, the'dioctyl ester, sold commercially under thedesignation Aerosol 0T (American Cyanamid Corp., N.Y.).

In the formulation of the employed within the following approximateranges, the amounts shown being stated in parts by volume.

Ingredients: Parts by .volume Trichloroethylene 250-350 Methylenechloride 40-60 Ethylene glycol diacetate 40-60 Aerosol OT, 25% 1-3 Apreferred primer formulation is as follows:

Trichloroethylene 300 Methylene chloride 50 Ethylene glycol diacetate 50Aerosol OT, 25% 2 The foregoing preferred primer formulation containsfrom about 40-60% by weight of Penton powder, preferably about 50%. Whenapplied to a smooth steel surface to form a 10-12 mil wet film, andfused for minutes at about 380-450 F., it forms a 3.5-4 mil fused film,which is continuous, homogeneous, clear or silvery in appearance, withexcellent adhesion as evidenced by bend, impact and knife adhesion testsand with no craters or pin holes to be seen under 20-powermagnification. The fused dry film can be air cooled or water quenchedwithout film shrinkage or pulling away from the metal. After quenchingit may be coated directly with the chlorinated polyether coatingcomposition of the invention previously described. The two coatings willfuse together in a homogeneous film without discontinuities and withoutany evidence of metal corrosion resulting from the aqueous character ofthe top coat. Total adhesion is excellent as indicated by bend, impactand knife tests.

The following examples serves to illustrate the practice of theinvention, but are not to be regarded as limiting:

Example 1.-Preparation of chlorinated polyether top coat dispersion 750grams of chlorinated polyether polymer (Penton) which were unpigmented,were ground to a fineness such that all passed through an 80 mesh sieve.

primer these ingredients are surface porosity,

The Penton powder was gradually added to 600 ml. of this solution withvigorous stirring and a homogeneous dispesion was obtained. To theresulting dispersion were added with stirring 15 ml. of isopropylalcohol, yielding a total volume of dispersion of approximately 750 ml.The dispersion thus obtained was ready for spray application.

Example 2.-Preparation of primer dispersion A diluent mixture wasprepared having the following composition:

Trichloroethylene 300 Methylene chloride u 50 Ethylene glycol diacetate50 Aerosol OT (25% clear) 1.6

To 250 ml. of the above mixture'there were added 200 grams of Pentonpowder, particle size minus 70 mesh, while stirring with the mechanicalmixer. After settling for 72 hours, the proportion of supernatant liquidobtained was about 2%.

Example 3.Application of coating system to tank car interior The tank ofa railway tank car was prepared for coating by first assuring that allwelds were full, smooth and continuous and free from surfaceimperfections such as cracks, unfilled craters, overlaps, and sharpcorners, burrs and edges. If necessary, the tank may be then heated forabout 4 hours at a metal temperature of about 500 F.i50 F. to remove oiland foreign matter by volatilization, in a suitable oven. Thereafter,the interior of the tank, including all the surfaces to be coated, wasblast cleaned to white metal using a suitable abrasive, and thereafterthe tank was thoroughly cleaned of blast residues.

Immediately following blast cleaning, and before any rust could form,the interior of the tank was sprayed with the primer coat of Example 2,care being taken to remove beforehand any traces of condensed moisture.The tank was maintained at about 50 F. or over during primerapplication. After ventilation to remove solvent and coating vapors, theprimer was cured by heating at 390 F., and inspected.

The polymer dispersion prepared for spraying as described in Example 1was then sprayed on the primer with the Binks spray gun mentioned inC01. 4, connected to a pressure feed tank having a motor drivenagitator. The temperature of the tank to be coated was maintained at 50F. or higher and the dispersion temperature between 65 F. and F. Thedispersion was applied by repeated passes of spraying until an adequatewet film thickness had built up. Measurements of wet film thickness weremade at intervals with a wet film gauge, and depressions made by thegauge were filled and smoothed. The wet film thickness of the coatingaveraged about 60 mils.

The wet film coating was dried and cured by oven heating. The oven washeated to maintain the tank at a temperature between 380 F. and 450 F.for a period of 75 minutes. No sagging, film degradation,discontinuities or bubbling were observed in the fused film afterremoval from the oven and quenching. The method of the invention has theadvantage that additional coatings may be applied if desired to attaingreater film thicknesses without any impairment of adhesion and otherfavorable properties.

' applied to the .directly on the At the end of the curing period, thetank was removed from the oven and rapidly quenched by a water sprayexterior of the-tank to coolit to below about 200 F., within aperiod ofabout 20 minutes after removal from the oven. When the exterior tanktemperature was reduced to about 200 F., and the film was then below itssoftening temperature, water was sprayed film to complete the quenching.The quenching produced a glossy tallization of the polymer. 1 p Y 7 Tankcars lined as described in Example 3 are in commercial use and providesuperior corrosion protection with a greater variety of chemicallading's than has been previously achieved.

.What is claimed is: 1. A coating composition comprising a dispersion ofa finely divided chlorinated oxetane (polyether)" polymer in an aqueousmedium including water, from about 0.0007 to about 0.08 part per 100anionic surfactant, an ester of a polyhydric alcohol with a loweraliphatic monocarboxylic acid in an amount between about 10 and about 20parts per 100 parts of water, from about 0.05 to about 0.30 part per 100parts surface and retarded crysparts of water of an of water of a watersoftener, and between about 10 and about 50 parts per 100 parts of waterof a lower aliphatic alcohol which is more volatile than water.

2. The composition of claim 1 in which the ester is ethylene glycoldiacetate.

3. The composition of claim 1 in which the alcohol is isopropyl alcohol.

4. The composition of claim 1 in which the surfactant is sodium dioctylsulfosuccinate.

5. Method for the preparation of a sprayable chlorinated oxetane(polyether) polymer coating composition which comprises the steps ofhomogeneously dispersing a finely divided chlorinated oxetane(polyether) polymer in an aqueous medium including water, from about0.0007 to about 0.08 part per 100 parts of water of a surfactant, anester of a polyhydric alcohol with a lower aliphatic monocarboxylic acidin an amount between about 10 and about 20 parts per 100 parts'of water,and from about 0.05 to about 0.30 part per 100 parts of water of a watersoftener, and then incorporating therewith between about 10 and aboutparts per parts of water of a lower aliphatic alcohol which is morevolatile than water. a 1 i 6. A coating composition comprisingadispersion of a finely divided chlorinated oxetane polymer in anorganic liquid medium including from about 250 to about 350 parts byvolume of trichloroethylene, from about 40 to about 60 parts by volumeof methylene chloride, from about 40 to about 60 parts by volume of anester of "a polyhydric alcohol with a lower aliphatic monocarboxylicacid, and from about 1 to about 3 parts by volume of a 25% by weightsolution of ananionic surfactant.

7. The composition of claim 6 in which the ester is ethylene glycoldiacetate.

References Cited I UNITED STATES PATENTS 2,872,428 2/1959 Schroeder260-29.2 2,947,722 3/1960 Boardman 260-3'1.6 3,061,566 10/1962 Kass Cl.al. 260-29.2 3,205,207 9/ 1965 Vandenberg 260-29.2 3,242,115 3/1966McGary 26029.2

MURRAY TILLMAN, Primary Examiner.

5 I C. BLEUTGE, Assistant Examiner.

